1. Field of the Invention
The present invention relates to a mirror device for a vehicle.
2. Description of the Related Art
PRIOR ART 1
In a mirror device for a vehicle, such as an electrically powered housable-type door mirror device, a mirror stay is fixed to a side of the vehicle body so as to extend in a substantially transverse direction from the vehicle, and a mirror main body portion is supported by the mirror stay such that the mirror main body can swing between a housed position and a position for viewing. This type of conventional door mirror device 100 is illustrated in FIGS. 18 to 21 and a brief description thereof follows.
As illustrated in FIG. 18, a stand 104 whose axial direction is a substantially vertical direction of a vehicle, is fixed on a mirror stay 102 which is fixed at a side of the vehicle. An electrically powered housing unit 106 is provided on the rotation shaft 104A of the stand 104, so as to be rotatable about the axis of the shaft. A mirror main body portion 110 comprising a mirror 108 and the like is connected to and supported by the electrically powered housing unit 106.
When a driving motor inside the electrically powered housing unit 106 operates, it works to rotate a gear plate 112 (See FIG. 20), which is axially supported by the rotation shaft 104A, via a gear mechanism. However, the gear plate 112 is always held so that it does not rotate with respect to the rotation shaft 104A. Thus, the electrically powered housing unit 106 itself rotates around the rotation shaft 104A. Since the mirror main body 110 is connected to and supported by the electrically powered housing unit 106, the mirror main body 110 rotates, along with the electrically powered housing unit 106, between the housed position and the position for viewing.
The schematic structure of a case 114, which forms the exterior of the electrically powered housing unit 106, will be described with reference to FIGS. 19 and 20.
FIG. 19 shows a schematic plan view of the case 114, which forms the exterior of the electrically powered housing unit 106 in the door mirror device 100. FIG. 20 shows a longitudinal section view of the case 114. A cylindrical support shaft portion 116 is erected at the left side, in the drawing, of the top surface of the case 114, and a circular concave portion 118 is formed around the support shaft portion 116. The rotation shaft 104A of the stand 104 is inserted inside the support shaft portion 116, and the case 114 is axially supported by the rotation shaft 104 so as to be rotatable. In addition, the gear plate 112, which applies anti-drive force to the electrically powered housing unit 106 and the mirror main body 110, is held so as to be fixed at the top end side of the support shaft portion 116.
In the electrically powered housing unit 106 having the above-described structure, the load of the electrically powered housing unit 106 and the mirror main body 110 must be supported by the support shaft portion 116 of the case 114. However, the strength of the support shaft portion 116 of the case 114 may be insufficient. Thus, external forces such as vehicle vibrations act on the door mirror device 100 and, as indicated by the arrow in FIG. 21, the mirror main body 110 vibrates in a substantially longitudinal direction of the vehicle, about a center in the vicinity of the support shaft portion 116 (the vicinity of the base of the stand 104). In order to limit this type of vibration, increasing the rigidity of the support shaft portion 116 has been considered. In order to do this, the plate thickness of the case 116 and/or the bottom portion 114A of the case 114 can be increased, thereby reinforcing the case 114. However, if this is done, there is the possibility that problems will be caused such as the generation of shrinkage and warping on a surface of the mirror. Also, it may be necessary to increase the number of cycles in the production process, leading to increased production costs.
PRIOR ART 2
Door mirror devices are usually equipped with a housing mechanism, and the housing mechanism includes a stand which is fixed to the vehicle side. The stand is provided so as to be integral with a support shaft.
The housing mechanism is equipped with a case member, and the case member is supported by the support shaft so as to be rotatable. The case member is connected to a mirror for viewing the rear of the vehicle and the case member always swings together with the mirror.
A motor base is fixed in an inner portion of the case member and a motor is fixed to the upper side of the motor base by screws. A motor output shaft passes through the motor base, and a worm gear is press-inserted onto the motor output shaft through the lower side of the motor base. As a result, the worm gear is swung by the motor being driven.
A helical gear meshes with the worm gear and the helical gear is rotated by the rotation of the worm gear. Thus, a rotational force is applied to the support shaft and the case member is rotated by anti-rotational force. The mirror can thus be housed or swung out for viewing.
However, with this type of door mirror device, the worm gear is press-inserted onto the motor output shaft, and is not movable in an axial direction with respect to the motor output shaft. As a result, there is a problem that the motor output shaft receives a sliding force from the worm gear, and this reduces the life span of the motor.
In order to solve this problem, door mirror devices are provided in which the motor output shaft and the worm gear are separate, and the worm gear is not rotatable with respect to the motor output shaft, but is movable in the axial direction thereof.
However, in this type of device, there is a tendency for the worm gear to displace in a perpendicular direction with respect to the motor output shaft. As a result, the sound of the operation between the worm gear and the helical gear becomes very loud and in some cases the worm gear may skid.
PRIOR ART 3
Further, in the door mirror device described above, the stand has a pair of stand concavities which are provided on a circle having the support shaft at the center thereof. The respective end portions of the stand concavities project upwards and face each other.
A gear plate is rotatably disposed around the support shaft which rotatably supports the case member, and a rotational force is applied to the gear plate by the motor being driven. The upper surface of the gear plate is provided with insertion convexities, which project upwards.
A clutch plate is disposed around the support shaft above the gear plate, and the clutch plate is not rotatable with respect to the support shaft. Insertion concavities are provided at a lower surface of the clutch plate, and end portions of the insertion concavities project downwards. The insertion convexities of the gear plate are inserted into these insertion concavities and as a result, the clutch plate meshes with the gear plate.
A compression coil spring is penetrated by the support shaft above the clutch plate, and push nuts are fixed on top of the compression coil spring. The compression coil spring is anchored by the push nuts, and the compression coil spring urges the clutch plate.
A pair of case convexities, formed on a circle having the support shaft at the center thereof, are provided at a lower portion of the case member. Each of the case convexities projects downwards, and they face each other.
When a rotational force is applied to the gear plate by the motor being driven, the clutch plate blocks the rotation of the gear plate. As a result, the case member is rotated by anti-rotational force exerted at the gear plate, and the mirror swings in a housing direction or in a viewing direction. Also, when the end portions of the case convexities engage with the end portions of the stand concavities, the case member is anchored, and the mirror can be stopped at the housed position or at the position for viewing.
On the other hand, if an external force exceeding a predetermined value acts on the case member, the urging force of the compression coil spring is resisted and the insertion convexities are disengaged from the insertion concavities. By the gear plate and the case member swinging with respect to the clutch plate, impact of the force can be ameliorated and damage to the gear plate is prevented.
However, in this type of door mirror device, end portions of all of the case convexities, the stand concavities, the insertion convexities and the insertion concavities are inclined surfaces having an upper area and lower area which are co-planar with each other. As a result, when the end portions of the case convexities engage with the end portion of the stand concavities, if the case convexities and the stand concavities undulate, they are connected linearly. Also, when the insertion convexities are inserted into the insertion concavities, or when insertion convexities and insertion concavities are disengaged, if the end portion of the insertion convexities and the end portion of the insertion concavities undulate, the insertion convexities and the insertion concavities are connected linearly. As a result, the case convexities, the stand concavities, the insertion convexities and the insertion concavities become worn and the durability of the mirror device is poor.
Since two sets of the case convexities and stand concavities are arranged on the same circle, whose center is the support shaft, when the end portions of the case convexities are engaged with the end portions of the stand concavities, the pressure which both the case convexities and the stand concavities receive is large and thus durability is poor. Also, when the end portions of the case convexities are engaged with the end portions of the stand concavities, the case member may rattle on the stand and as a result the mirror also tends to rattle.